This invention relates to sound systems and more particularly to apparatus for separating two audio signals appearing on two separate input channels into output signals appearing on at least three output channels. The apparatus is particularly useful for separating the audio signals recorded on two tracks of motion picture film into three or more separate channels for a theatre sound system.
Under today's standards, most commercial motion picture film is provided with two sound tracks on which are recorded two separate audio signals for producing a stereophonic sound effect. In the production of many films, the producer and director of the picture would like to create sounds and sound effects which heretofore have not been possible on a two channel sound system. For example, in addition to the normal left and right channels which provide directional sound effects, it is sometimes desirable to surround the theatre patrons with sound and special sound effects. Also, it often is desirable to provide a third or center channel in addition to the normal left and right channels. The center channel is desirable, for example, during normal speech when the sound is effectively monaural. In the past, a center channel sometimes has been produced simply by combining the audio signals appearing on the left and right channels. Signals are applied to the center channel simultaneously with the left and right channels. This has not been completely satisfactory since it reduces the directional effect of the sound when all three channels are operating.